Input and Output in Python

1. Output (Print Statement):

The print() function is used to display output to the console.

name = "Alice"
age = 25

# Displaying variables
print("Name:", name)
print("Age:", age)

# Concatenation in print
print("Name:", name, "Age:", age)

# Formatted output (using f-strings in Python 3.6 and later)
print(f"Name: {name}, Age: {age}")

2. Input:

The input() function is used to get user input from the console. Note that input() returns a string, so you might need to convert it to the desired data type.

# Getting user input
user_name = input("Enter your name: ")

# Displaying the input
print("Hello, " + user_name + "!")

3. Formatted Output (String Formatting):

You can format strings using placeholders or the format() method.

Using Placeholders:

name = "Bob"
age = 30

# Placeholder formatting
print("Name: %s, Age: %d" % (name, age))

Using format() Method:

# Using format method
print("Name: {}, Age: {}".format(name, age))

4. Formatted Output (f-strings):

f-strings (formatted string literals) provide a concise way to embed expressions inside string literals.

# Using f-strings
print(f"Name: {name}, Age: {age}")

5. File Input and Output:

You can read from and write to files using the open() function.

Writing to a File:

# Writing to a file
with open("example.txt", "w") as file:
    file.write("Hello, Python!")

Reading from a File:

# Reading from a file
with open("example.txt", "r") as file:
    content = file.read()

6. Separator and End Parameters in print():

The print() function allows specifying the separator between printed items and the ending character.

# Separator and end parameters
print("apple", "banana", "orange", sep=", ", end=".\n")

7. Formatted Output with Precision:

Control the precision of floating-point numbers when printing.

pi_value = 3.141592653589793

# Formatting with precision
print(f"Value of pi: {pi_value:.2f}")

8. Redirecting Output to a File:

You can redirect the print() output to a file by changing the sys.stdout stream.

import sys

# Redirecting output to a file
with open("output.txt", "w") as file:
    sys.stdout = file
    print("This will be written to the file.")
    sys.stdout = sys.__stdout__  # Resetting the stream

9. Error Output:

The print() function can be used to output to the standard error stream (sys.stderr) for error messages.

import sys

# Error output
print("Error: Something went wrong.", file=sys.stderr)

Understanding input and output operations is fundamental for creating interactive and dynamic Python programs. In the next sections, we’ll explore how to use these concepts in various scenarios and applications.